Cotylorhiza tuberculata is a common symbiotic scyphozoan in the Mediterranean Sea. The medusae occur in extremely high abundances in enclosed coastal areas in the Mediterranean Sea. Previous laboratory experiments identified thermal control on its early life stages as the driver of medusa blooms. In the present study, new ecological aspects were tested in laboratory experiments that support the pelagic population success of this zooxanthellate jellyfish. We hypothesized that planulae larvae would have no settlement preference among substrates and that temperature would affect ephyra development, ingestion rates and daily ration. The polyp budding rate and the onset of symbiosis with zooxanthellae also were investigated. Transmission electron microscopy revealed that zooxanthella infection occurred by the polyp stage. Our results showing no substrate selectivity by planulae and high polyp budding rates in high temperatures suggest increased benthic polyp populations, which would lead to higher medusa abundances. Rates of transition from ephyrae to medusae and the feeding of early medusa stages also increased with temperature. Continuing changes in coastal ecosystems such as future climate warming and marine construction may lead to increased populations of jellyfish to the detriment of fish globally.